Enable build with Clang for KMSAN kernel

SPECS/kernel-6.1.spec

@@ -3,6 +3,20 @@
 # Disable LTO in userspace packages.
 %global _lto_cflags %{nil}
 
+# Option to enable compiling with clang instead of gcc.
+%bcond_with toolchain_clang
+
+%if %{with toolchain_clang}
+%global toolchain clang
+%endif
+
+# Compile the kernel with LTO (only supported when building with clang).
+%bcond_with clang_lto
+
+%if %{with clang_lto} && %{without toolchain_clang}
+{error:clang_lto requires --with toolchain_clang}
+%endif
+	
 # The libexec directory is not used by the linker, so the shared object there
 # should not be exported to RPM provides.
 %global __provides_exclude_from ^%{_libexecdir}/kselftests
@@ -49,7 +63,7 @@
 %endif
 
 # Set pkg_release.
-%global pkg_release 3%{?buildid}.%{?lvc}%{?dist}.inferit.fuzzing
+%global pkg_release 4%{?buildid}.%{?lvc}%{?dist}.inferit.fuzzing
 
 # Architectures upon which we can sign the kernel
 # for secure boot authentication.
@@ -156,6 +170,21 @@
 %define _use_vdso 0
 %endif
 
+%if %{with toolchain_clang}
+%ifarch aarch64 noarch
+%global llvm_ias 0
+%else
+%global llvm_ias 1
+%endif
+%global clang_make_opts HOSTCC=clang CC=clang LLVM_IAS=%{llvm_ias}
+%if %{with clang_lto}
+%global clang_make_opts %{clang_make_opts} LD=ld.lld HOSTLD=ld.lld AR=llvm-ar NM=llvm-nm HOSTAR=llvm-ar HOSTNM=llvm-nm
+%endif
+%global make_opts %{make_opts} %{clang_make_opts}
+# clang does not support the -fdump-ipa-clones option
+%global with_ipaclones 0
+%endif
+
 #
 # Packages that need to be installed before the kernel is installed,
 # as they will be used by the %%post scripts.
@@ -185,6 +214,16 @@ BuildRequires: gzip, hmaccalc, hostname, kernel-rpm-macros >= 185-9, kmod, m4, m
 BuildRequires: patch, perl-Carp, perl-devel, perl-generators, perl-interpreter, python3-devel
 BuildRequires: redhat-rpm-config, tar, which, xz
 
+%if %{with toolchain_clang}
+BuildRequires: clang
+%endif
+
+%if %{with clang_lto}
+BuildRequires: llvm
+BuildRequires: lld
+%endif
+
+
 %ifarch x86_64 aarch64
 BuildRequires: bpftool, openssl-devel
 %endif
@@ -599,6 +638,7 @@ pathfix.py -i "%{__python3} %{py3_shbang_opts}" -n -p \
 	tools \
 	scripts \
 	Documentation \
+	scripts/clang-tools \
 	2>&1 | grep -Ev 'recursedown|no change'
 
 mv COPYING COPYING-%{version}-%{release}
@@ -665,6 +705,13 @@ cat rheldup3.pem rhelkpatch1.pem rhelimaca1.pem > certs/rhel.pem
 
 cd configs/
 
+ %if %{with clang_lto}
+for i in *aarch64*.config *x86_64*.config; do
+	sed -i 's/# CONFIG_LTO_CLANG_THIN is not set/CONFIG_LTO_CLANG_THIN=y/' $i
+	sed -i 's/CONFIG_LTO_NONE=y/# CONFIG_LTO_NONE is not set/' $i
+done
+%endif
+
 for i in *.config; do
 	sed -i 's@CONFIG_SYSTEM_TRUSTED_KEYS="*"@CONFIG_SYSTEM_TRUSTED_KEYS="certs/rhel.pem"@' $i
 done
@@ -774,9 +821,15 @@ BuildKernel() {
     perl -p -i -e "s/^CONFIG_BUILD_SALT.*/CONFIG_BUILD_SALT=\"%{KVERREL}\"/" .config
 
     %if %{with_std}
+    if [ $Variant == "kmsan" ]; then
+    %{make} %{clang_make_opts} %{?_smp_mflags} ARCH=%{bldarch} %{make_target}
+
+    %{make} %{clang_make_opts} %{?_smp_mflags} ARCH=%{bldarch} modules || exit 1
+    else
     %{make} %{?_smp_mflags} ARCH=%{bldarch} %{make_target}
 
     %{make} %{?_smp_mflags} ARCH=%{bldarch} modules || exit 1
+    fi
     
     %ifarch aarch64
     %{make} %{?_smp_mflags} ARCH=%{bldarch} dtbs
@@ -851,8 +904,11 @@ BuildKernel() {
 
     # Override mod-fw because we don't want it to install any firmware.
     # We'll get it from the linux-firmware package and we don't want conflicts.
+    if [ $Variant == "kmsan" ]; then
+    %{make} %{clang_make_opts} %{?_smp_mflags} ARCH=%{bldarch} INSTALL_MOD_PATH=$RPM_BUILD_ROOT modules_install KERNELRELEASE=$KernelVer mod-fw=
+    else
     %{make} %{?_smp_mflags} ARCH=%{bldarch} INSTALL_MOD_PATH=$RPM_BUILD_ROOT modules_install KERNELRELEASE=$KernelVer mod-fw=
-    
+    fi
     # Add a noop %%defattr statement because rpm doesn't like empty file list files.
     echo '%%defattr(-,-,-)' > ../%{name}${Variant:+-${Variant}}-ldsoconf.list
 
@@ -1746,6 +1802,9 @@ fi
 %endif
 
 %changelog
+* Mon Feb 10 2025 Eduard Basov <ebasov@msvsphere-os.ru> - 6.1.124-4.lvc13.inferit.fuzzing
+- Added build with clang 
+
 * Fri Feb 07 2025 Eduard Basov <ebasov@msvsphere-os.ru> - 6.1.124-3.lvc13.inferit.fuzzing
 - Added more options
 - Disable build with GCC 13